Various physiological stimuli, e.g., hormones, neural excitation and pharmacological agents can influence glycogen metabolism in a variety of tissues by altering a cascade of enzymatic relations. Our objective is to show how enzyme catalyzed covalent modification reaction occur and are regulated to (1) better understand glycogen metabolism in normal, healthy tissues and in cases where metabolic disturbances occur due to deficiences of insulin or vitamin B6, and (2) provide a basis how post-translational modification of proteins can control other important cellular processes. Specifically four major research areas are proposed: I. Enzyme Catalyzed Covalent Modification of Glyoogen Phosphorylase - Relationships of Chemical and Physical Changes to Regulatory Phenomena. II. Phosphorylase Kinase - A Stucy of Structural, Chemical, Catalytic and Regulatory Features. III. Enzyme Catalyzed Covalent Modification Reactions of Phosphoprotein Phosphatases - Mechanism and Specificity of the Reactions.